A beamsplitter is an optical device that separates a beam of light into two or more different beams of light. Beamsplitters have a variety of different and useful applications. For example, beamsplitters can be used in cameras and projectors and can be used in interferometry just to name a few. FIGS. 1A-1B show schematic representations of two types of commonly used beamsplitters. FIG. 1A shows a top and an isometric view of a cube beamsplitter 100. The cube beamsplitter 100 includes a first triangular prism 102 and a second triangular prism 104. The hypotenuse surfaces of the prisms 102 and 104 are made parallel and planar and are coated with a layer of partially reflective material 106, such as silver or aluminum. The hypotenuse of the prisms 102 and 104 can be cemented together with an adhesive having substantially the same refractive index as the prisms 102 and 104. The thickness of the layer 106 can be adjusted to allow desired fractions of light to be transmitted and reflected. As shown in FIG. 1, an incident beam of light 108 enters the cube beamsplitter 100 substantially perpendicular to a planar surface. The layer 106 splits the incident beam 108 into a transmitted beam 110 that emerges from the cube beamsplitter 100 in the same direction as the incident beam 108 and a reflected beam 112 that emerges from the cube beamsplitter 100 substantially perpendicular to the incident beam 108.
FIG. 1B shows a side view of a plate beamsplitter 120. The plate beamsplitter 120 includes a single plate 122 of glass with one surface of the plate 122 coated with a partially reflective layer 124 and the opposite surface can be coated with an anti-reflective layer. As shown in FIG. 1B, the plate 122 is oriented at 45° to an incident beam of light 126. The layer 124 reflects a first portion of the incident beam 126 to produce a reflected beam 128 that is substantially perpendicular to the incident beam 126. A second portion of the incident beam 126 enters the plate 126 producing a refracted beam 130 that is refracted upon emerging from the plate 122 to give a transmitted beam 132 oriented substantially parallel to the incident beam 126. Due to refraction of the beam entering the plate 120, the path of the transmitted beam 132 is shifted below the path of the incident beam 126, which is called the “beam offset.” The magnitude of the beam offset is proportional to the thickness of the plate 122.
Although the beamsplitters 100 and 120 have been employed successfully in a number of different devices, they have a number of disadvantages. For example, cube beamsplitters are typically bulky and therefore difficult to insert into small optical devices, while the plate beamsplitter typically requires using a very thin glass or acrylic plate 122 to reduce the beam offset. However, a very thin plate 122 can be fragile and requires complicated fabrication processing. Accordingly, beamsplitters that are not as bulky and do not have significant beam offset are desired.